[GuB-42]

It should be easy to test. Just set the alarm at a random time. Something like 5 to 10 minutes earlier.

To do it blindly you can have someone else do it, scramble the clock, use an app,...

[henrikschroder]

In my experience, it only works if I know the time and want to wake up at that time. I'm more likely to experience it the more important it is that I wake up on time. If I have to wake up for travel purposes, it's almost guaranteed that I'll wake up before the alarm.

[thewhitetulip]

Please read the book "power of subconscious mind".

I had trained myself to fall asleep immediately after falling on bed and waking exactly at 6 without setting an alarm.